The deregulation of the electricity market, which gradually concerns aIl the countries in Europe, modifies considerably the technico-economic approach in the exploitation and the optimization of power systems. In this new context, power system specialists are more and more confronted with many challenges. The development of FACTS devices (Flexible AC System Transmission) opens new pro~pects for a better exploitation of power systems by their continuous and fast action on the various parameters. However, interaction phenomena can occur between these devices and also with other power system components such dynamic loads. This thesis, which deals with the analysis and the improvement of power systems dynamic security, was focused on the impact of the interaction between FACTS devices and dynamic loads. In this work, it was shown that power oscillations damping loops dimensioned by the eigensensitivity traditional techniques are not robust with respect to load model variations. To overcome these problems, a first method, based on the eigensensitivity but also taking into account the load model variations, was proposed. Two other more robust methods, based on techniques LMI, were implemented. The first one, based on a polytopic representation of the uncertain system, is appropriate for the case of unstructured uncertainties. The second, based on a representation LPV (linear parameter varying system), treats the case of structured uncertainties.
